Process for chemical vapor deposition of films on silicon wafers

ABSTRACT

A process for depositing films of uniform thickness on silicon wafers at a uniform deposition rate among all wafers processed at the same time. The wafers are vertically oriented and arranged in a spaced-apart mutually parallel fashion and are supported within a horizontally-oriented long quartz tube which is evacuated at one end by a vacuum pump. A heating element surrounding the tube heats the wafers supported within it. At least one type of reactant gas is introduced into the enclosure in a generally confined region below the wafers and between the wafer arrangement and a wall of the enclosure. The gas, which is directed upwards between adjacent wafers and dispersed across the entire surface of the wafers, chemically reacts to deposit a uniform film on the wafers. Unreacted and exhaust gases are evacuated from the enclosure by the vacuum pump in a horizontal direction of flow above the wafer arrangement.

BACKGROUND OF THE INVENTION

This invention is a process relating to the fabrication of integratedcircuits, and more specifically to the chemical vapor deposition of thinfilms on the silicon wafers which serve as the substrate of thecircuits.

In the fabrication of integrated circuits, several hundred circuits areformed side-by-side on a single silicon wafer which has been cut from along single crystal of silicon. Thin films of various materials whichserve as the active circuit elements are deposited on the silicon waferat various stages of the fabrication process. After each film isdeposited on the wafer, certain portions of the film are selectivelyremoved, usually by photolithography, so that only a predeterminedpattern of the film remains.

A conventional method for forming the various thin films on the wafersis by chemical vapor deposition. In this process, the wafers are placedin a "boat" in a spaced-apart mutually parallel arrangement. The boatcontaining the wafers is inserted into a long quartz tube which isevacuated at the exit end by means of a vacuum pump. The quartz tube issurrounded by a cyclindrical heating element which directs thermalradiation into the interior of the tube to heat the wafers. A reactantgas introduced at one end of the tube is forced to flow toward the exitend of the tube because of the vacuum pump. As the gas passes thewafers, a chemical reaction occurs and a product of that reaction isdeposited as a film on the wafers. In many instances more than onereactant gas is introduced so that a product of a chemical reactionbetween the two gases is deposited as a film on the wafers.

This conventional process for the chemical vapor deposition of films onsilicon wafers has several inherent disadvantages. Because the siliconwafers occupy only a relatively small part of the evacuated tube,considerable reactant gas must be introduced, only a portion of which isnecessary to form the thin film.

Since the gas is passing through the tube in a direction perpendicularto the wafer surfaces on which the film is to be deposited, the gas flowis interrupted and unpredictable flow characteristics are generatedwithin the tube. It is only because of a changing flow direction causedby the silicon wafers that gas is forced to travel between adjacentwafers and thus into contact with the wafer surfaces. This unpredictableflow pattern across the wafer surfaces often results in a lack ofuniform film thickness on each wafer.

The greatest localized volumetric rate of flow of gas and thus thefastest film deposition rate occurs near the first wafer contacted bythe flowing gas. In contrast, the last wafer in the wafer arrangementexperiences a substantially reduced rate of film deposition. In order tocompensate for variations in the rate of film deposition among wafers inthe boat, an inert carrier gas, such as nitrogen, is used to "carry" thereactant gas toward the exit end of the tube in order to enhance thedeposition rate on the end wafers in the wafer arrangement.Additionally, since film deposition rate is a function of wafertemperature, an increasing temperature profile is created along thelength of the wafer arrangement by varying the voltage to variouselements of the heating elements surrounding the tube. By maintainingeach wafer at a different temperature, with the temperature of thewafers increasing in the same direction of gas flow, the effect of thelocalized variation in volumetric gas flow rate on film deposition rateis compensated, and the rate of film deposition and thus the thicknessof the deposited film is maintained relatively uniform among the wafersin the boat.

One attempt has been made to improve the conventional chemical vapordeposition process by enclosing the wafer boat in a cylindricalcontainer having a plurality of holes on its outer surface. The end ofthe container facing the inlet for the reactant gas has a cover placedover it and the other end is open. As the gas enters from the inlet endof the tube, it changes direction and enters the holes in thecylindrical container where it passes between the silicon wafers. Thegas is removed from the tube by passing through the open end of thecontainer and out the exit end of the tube in a conventional manner.This process does not completely solve the problem of localized flowrate variations from one end of the wafer arrangement to the other end,and thus both a carrier gas and a temperature profile are required tocreate uniformity in film thickness within each wafer and from wafer towafer.

SUMMARY OF THE INVENTION

The invention is directed to and a process for the deposition of thinfilms on silicon wafers in which the wafers are supported in aspaced-apart parallel arrangement within an evacuated enclosure and thereactant gas is introduced into the enclosure in a generally confinedregion between the wafer arrangement and the wall of the enclosure. Asthe reactant gas is introduced into the confined region, it is forced toflow generally parallel to and between the wafers. Prior to passing intocontact with the wafer surfaces, however, turbulence is generated in theflowing gas in order to disperse the gas across the entire width of thewafer surfaces, thereby facilitating film deposition and uniform filmthickness on each wafer. After the gas has passed between the wafers andchemically reacted to deposit the films on the wafers, the unreacted andexhaust gases pass to the other side of the wafer arrangement and areremoved from the enclosure by flowing in a generally horizontaldirection toward the exit of the enclosure. During the above-describedflow of the reactant gas, the temperature of the wafers in the waferarrangement is maintained generally constant and equal by means ofheating elements located exterior of the evacuated enclosure. Because ofthe generally equal localized volumetric flow rates between adjacentwafers, the maintenance of the wafers at the same temperature issufficient to permit uniform film deposition among the wafers.

In one embodiment of the invention, the reactant gas is introducedhorizontally from both ends of the evacuated enclosure into the regionbelow the wafer arrangement, and is then directed vertically upward in agas curtain such that the localized volumetric rate of flow across theentire length of the gas curtain and thus across the entire length ofthe wafer arrangement is maintained generally constant, therebyresulting in generally the same volume of reactant gas being supplied tothe surface of each wafer. When two reactant gases are used in theprocess, each gas is introduced into the confined region below the waferarrangement. After introduction into that region, the gases chemicallyreact with one another and a product of that reaction is deposited as afilm on the wafers. In such a process, the flow rate of each reactantgas is controlled so that the ratio of total volumetric flow rate of thetwo gases is maintained at a predetermined value.

The apparatus for use in the above-described process comprises generallyan evacuated enclosure and means for maintaining the pressure within theenclosure substantially below atmospheric, means for supporting thewafers within the enclosure such that the wafer supporting means and thelower portion of the enclosure define a generally confined region belowthe wafer arrangement, means for introducing the reactant gas into theconfined region below the wafer arrangement and for directing the gasflow generally vertically upward, means near the lower portion of thewafer arrangement for generating turbulence in the upwardly flowing gas,and means located exterior of the enclosure for directing thermalradiation into the enclosure to heat the wafers as the gas is beingintroduced.

The wafer supporting means comprises generally a cylindrically shapedcontainer having a plurality of longitudinally extending openings on itscylindrical surface which allow the gas to flow through the container ina direction generally perpendicular to its longitudinal axis andparallel to the wafer surfaces. Two parallel sidewalls extend the lengthof the container and project generally tangentially outward fromopposite sides of the cylindrical surface of the container. When theoutermost edges of the two sidewalls are placed into contact with thebottom of the evacuated enclosure, a generally confined region isdefined below the wafers, which are supported inside the container. Thewafers are supported inside the container in a spaced-apart mutuallyparallel arrangement and are oriented perpendicular to the longitudinalaxis of the container. The longitudinal openings in the container, inone embodiment of the invention, are defined by long, parallelspaced-apart rods located about the cylindrical surface of thecontainer. The rods have a circular cross-section so that as theupwardly flowing gas contacts the rods, turbulence is generated by thegas flowing around the rods and into the openings between adjacent rods.This turbulence disperses the gas and causes it to flow across theentire width of the wafer surfaces, thereby enhancing the uniformity ofthe thickness of the film deposited on each wafer. After the gas haspassed between the wafers and approaches the rods on the other side ofthe cylindrical surface of the container, additional turbulence isgenerated to further disperse the gas across the entire width of thewafer surfaces. There is sufficient space between the container and thetop of the enclosure to allow the unreacted and exhaust gases to beremoved in a horizontal direction toward the exit end of the enclosure.

The means for introducing the reactant gas into the confined regionbelow the wafers comprises generally a pair of horizontally orientedconduits extending through both ends of the evacuated enclosure andpassing into the region between the wafer supporting means and thebottom of the enclosure. On each of the conduits, near the portion ofthe conduit located below the wafer supporting means, is alongitudinally extending slot for the exit of the reactant gas which isintroduced from outside the enclosure and through the conduit. In oneembodiment of the apparatus, the reactant gas is introduced fromopposite ends of the conduit and then passes vertically upward throughthe slot as a curtain of upwardly flowing gas. When two reactant gasesare required, each gas is introduced through a separate conduit.

Thus, with the present invention the reactant gas is introducedimmediately into close proximity with the surfaces of the wafers and thevolumetric gas flow rate near each wafer is maintained generally thesame so that there is uniformity in the film thickness among the wafers.The invention thus eliminates a carrier gas and the necessity of heatingthe wafers in the arrangement to different temperatures, therebyreducing the amount of energy used in the process. Further, since thegas is introduced near the wafers where it immediately reacts to formthe film, less reactant gas is required than in the conventional processin which large amounts of unused reactant gas are removed from theenclosure by the vacuum pump. Additionally, since the gas is dispersedand spread over the entire width of the wafer surfaces, the thickness ofthe film deposited on each wafer is uniform.

For a fuller understanding of the nature and advantages of theinvention, reference should be made to the ensuing detailed descriptiontaken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view of the invention illustrating a portion of theinvention in block diagram;

FIG. 2 is a side cut-away view of the evacuated enclosure on theinvention disclosing the means for supporting the silicon wafers; and

FIG. 3 is a view of section 3--3 of FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring first to FIG. 1, the invention compromises generally anenclosure, such as elongated quartz tube 10, means for evacuating theenclosure, such as vacuum pump 12 which is connected to tube 10 at itsexit end 14, a heating element 16 surrounding tube 10 and electricallyconnected to a temperature controller 18 for heating the silicon wafers,means for supporting the wafers within the enclosure (FIGS. 2 and 3),and a reactant gas flow system which includes gas tanks, flowtransducers, valves, and conduits for injecting the reactant gas intothe interior of the enclosure.

The evacuated enclosure is preferably an elongated cylindrically shapedquartz tube which has an entrance 13 connected to a hinged door 20 andan exit 14 connected to vacuum pump 12 by means of a stainless steelconduit 22. During the film deposition process, vacuum pump 12 isoperated at essentially full speed to maintain the pressure within thetube substantially below atmospheric. Heating element 16, shown insection in FIG. 1, is wrapped as a coil around tube 10, and directsthermal radiation through the radiation-permeable quartz tube 10 to heatthe wafers contained inside.

The above-described quartz tube 10, heating coil 16 and its temperaturecontroller 18, and vacuum pump 12 connected to tube 10, comprise themajor portions of the apparatus used in the conventional chemical vapordeposition process on silicon wafers. In the conventional process, door20 is opened and the silicon wafers, which are supported on a "boat" ina spaced-apart mutually parallel arrangement, are inserted into theinterior of tube 10. Reactant gas which is injected through openings(not shown) in door 20, passes from entrance 13 to exit 14, and isevacuated by vacuum pump 12. During travel through tube 10, the gaspasses in a direction generally perpendicular to the wafers supported inthe boat. The temperature controller 18 maintains the temperature alongthe length of the wafer boat according to a temperature profile whichincreases in the direction of gas flow so that each of the wafers isheated to a temperature higher than the wafer just upstream. In thismanner variations in local volumetric flow rate and thus variations inlocal chemical reaction rate are compensated to provide a generallyuniform film thickness among the wafers within the boat. Additionally aninert carrier gas is frequently used to "carry" the reactant gas towardexit 14 of tube 10.

In the present invention, in contrast to the conventional process, thereactant gas or gases are introduced on the inside of the enclosure andare forced to flow parallel to the wafers. Referring again to FIG. 1,when only one reactant gas is used in the process, the gas from supplytank 30 passes through stainless steel tubing 36, flow transducer/valve38, and valve 40, where it is divided into two paths, i.e. tubing 42 and44. The gas is then directed from opposite ends of the tube 10 intoquartz conduit 46 located inside tube 10. If a second reactant gas,which is contained in supply tank 32, is required, it passes throughtubing 50, flow transducer/valve 52, and valve 54, where it is dividedinto two paths, i.e. tubing 55 and 57. The second reactant gas is thenintroduced from opposite ends of the tube 10 into quartz conduit 56.Conduits 46, 56 inside tube 10 serve as the means for introducing thereactant gases into the interior of tube 10 and for directing the gasgenerally parallel to the spaced-apart wafers in the wafer arrangement.As shown in FIG. 1, conduits 46, 56 contain elongated slots 60, 62,respectively, of constant width for introducing the gas in a directiongenerally parallel to the wafers in the wafer arrangement. A third gastank 34 in the gas flow system is also operatively connected byassociated stainless steel tubing to supply line 50 and includes its ownflow transducer/valve 64. Tank 34 contains a dopant gas which, ifrequired, is mixed with the second reactant gas prior to itsintroduction into tube 10. Each of the flow transducer/valves 38, 52,and 64 are electrically connected to a programmable flow controller 61which permits predetermined flow rates to be selected and controlled forall of the gases. Thus, the ratio of volumetric flow rates between thefirst and second gases and the amount of dopant gas mixed with thesecond reactant gas can be preselected and controlled. Each of thetransducer/valves 38, 52, and 64 is a conventional thermal mass flowcontroller in which the desired flow rate is selected by varying thereference voltage to an operational amplifier which controls amechanical valve. The reference voltages are selected throughprogrammable flow controller 61. Once the gas flow rates are selected onthe programmable flow controller 61, the transducer/valves maintain therespective flow rates within a range about their respective preselectedvalves.

Referring now to FIGS. 2 and 3, the novel means for supporting thesilicon wafers in the evacuated enclosure is illustrated. The wafersupporting means comprises generally a cylindrically-shaped container 70which has a plurality of longitudinally extending openings spaced aboutits cylindrical surface and parallel side walls 72, 74, extendingtangentially outward from the cylindrical surface of container 70. Theedges 73, 75 of walls 72, 74, are generally in contact with the bottomof tube 10 when container 70 is placed inside tube 10 (FIG. 3). Asillustrated in FIG. 2, a portion of sidewall 74 has been cut away toreveal conduit 56 within tube 10. Located behind conduit 56 in the sideview of FIG. 2, is conduit 46 (not shown). In the preferred embodimentof container 70, the longitudinally extending openings in cylindricalcontainer 70 are defined by spaced-apart rods 76 at the top portion androds 78 at the lower portion. Rods 76 and 78 are bonded to end plates77, 79, and an intermediate support plate (not shown), all of which aresemi-circularly shaped and oriented generally parallel to the wafers.Similiarly rods 78 are bonded to end plates 81, 83, and intermediatesupport plate (not shown). Thus container 70 is comprised of two halves.The top half, including rods 76 secured to end plates 77, 79 isremovable from the bottom half, including rods 78 secured to end plates81, 83, so that the wafers may be placed inside. As shown in FIG. 3, theparallel side walls 72, 74, extend generally tangentially outwardly fromthe outer surface of container 70 and have their outermost edges, 73, 75bonded to rods 86, 88 which are in contact with the bottom 90 of tube10. Container 70 is preferably constructed of quartz, which has theability to withstand high temperatures and which possesses a relativelylow coefficient of thermal expansion, but any material which has thesecharacteristics would function equally as well.

While the above described configuration is one embodiment of container70, alternatively the wafer supporting means may be constructed of acylindrical canister into which longitudinal openings are cut betweenportions of the outer wall of the canister.

It should be apparent from the above description that the region definedby bottom 90 of tube 10, the lower portion of container 70, and sidewalls 72, 74 is a generally confined space 89 below the parallelspaced-apart wafers retained within container 70. As shown in FIG. 3, atypical silicon wafer 92 is retained upright and oriented perpendicularto the longitudinal axis of container 70 by residing within a notch 96in a longitudinal guide rail 97. Also depicted in FIG. 3 is thecross-sectional view of conduits 46, 56, with their respective slots 60,62 through which the reactant gases are introduced. The elongated slots60, 62 direct the gas vertically upward into a gas curtain within theconfined region 89 beneath the wafers. It should be apparent thatalthough the embodiment shown in the drawings illustrates the confinedspace 89 being located below the wafer arrangement in container 70 anddiscloses introducing the gas so that it flows vertically upward, theinvention will function equally as well regardless of the location ofspace 89 within tube 10, provided that the gas introduced into space 89is directed to flow parallel to the wafers and through the spacesbetween the wafers to the other side of the wafer arrangement.

The apparatus as thus described can be better understood by consideringthe function of the respective component parts during the process fordepositing thin films on the silicon wafers. The wafers are first placedinto container 70 by removing the top half and inserting the wafers intothe notches on guide rail 97. The wafers as thus supported are paralleland spaced-apart in container 70, as depicted in FIG. 2. The top portionof container 70 is replaced and container 70 is inserted through opendoor 20 into tube 10. Container 70 with the spaced-apart waferssupported within it rests on the bottom 90 of tube 10 and the rods 86,88 connected to side walls 72, 74 are in contact with tube bottom 90.Container 70 is inserted far enough into tube 10 so that it is directlyabove slots 60, 62 in conduits 46, 56, respectively. Door 20 is closedand a seal between it and tube 10 is maintained by a rubber gasket (notshown). Quartz tube 10 is then evacuated by activating vacuum pump 12which maintains the pressure within tube 10 substantially belowatmospheric. The temperature for the silicon wafers is selected by meansof temperature controller 18 connected to heating element 16, whichdirects thermal radiation through the radiation-permeable wall of quartztube 10 into the interior where the temperature of the wafers iselevated. A "flat" temperature profile is selected on controller 18 sothat each of the wafers in the wafer arrangement is heated toessentially the same temperature. The volumetric flow rate of thereactant gas is selected by means of programmable flow controller 61and, if two reactant gases are required, the desired flow rates of bothgases are selected.

Assuming for purposes of this description of the process that silicondioxide is to be deposited upon the silicon wafers as a dielectricisolation layer on the completed integrated circuits, the first reactantgas from tank 30 is silane (SiH₄), and the second reactant gas from tank32 is oxygen (O₂). The programmable flow controller 61 connected totransducer/valves 38, 52 is programmed to permit the predetermined ratioof flow rates of silane and oxygen. The preselected flow rates aremaintained during the process by transducer/valves 38, 52. The processis automatically activated by programmable flow controller 61 whichbegins the flow of gas from gas tanks 30, 32 through respective valves40, 54 into opposite ends of respective conduits 46, 56. In thepreferred embodiment valves 40, 54 are adjusted so that the gas flows atgenerally equal rates into both ends of conduits 46, 56, respectively.The flow is thus diverted into each of the respective paths, e.g., intotubings 42 and 44 for the silane and into tubings 55 and 57 for theoxygen. Silane passes through tubings 42, 44 in opposite directionsthrough conduit 46 until it reaches slot 60 in conduit 46, after whichit is introduced into tube 10 as a generally vertically oriented gascurtain. In a similar manner, the oxygen gas from tank 32 is split intotwo paths by means of valve 54 and enters conduit 56 from oppositedirections until it is introduced vertically upward and parallel to thesilicon wafers through slot 62. The widths of slots 60, 62 for mostapplications may be generally between 0.005 inches and 0.020 inches. Ofcourse, since the widths of the slots affect the volumetric flow ratesof the gases and thus the film deposition rate, once the widths arechosen, tests would be conducted to determine the proper settings fortransducer/valves 38, 52. It should be noted that as the gases are beingintroduced into tube 10, vacuum pump 12 immediately evacuates tube 10and maintains the pressure within it substantially below atmospheric.Simultaneously, the silicon wafers are heated by heating coil 16 whichdirects thermal radiation through the wall of tube 10 to raise thetemperature of the wafers to a preselected valve. In establishing theinitial values for the flow rates of the gases, the pressure within tube10, the temperature of the silicon wafers, and the settings for valves40, 54, test runs are conducted to arrive at values which give theoptimum rate and uniformity of film deposition.

Referring again to FIGS. 2 and 3, the flow of gas within confined region89 after is has exited slots 60, 62 can be better understood. As thesilane and oxygen exit slots 60, 62, respectively, the gases aredirected into a generally vertically oriented gas curtain below thelower portion of container 70, specifically rods 78. Because theenclosure within tube 10 is almost completely a vacuum, upon exitingslots 60, 62, the gases rapidly expand within the generally confinedregion 89. The gases, which are injected with an initial velocity fromthe slots, are directed into contact with rods 78 beneath the wafers. Asthe gases contact rods 78, the flow is diverted into a plurality of gasstreams and turbulence is generated in the flow. The gases pass aroundrods 78 which disperse the gases across the width of the wafers. Asturbulence is generated and the gases dispersed, the silane and oxygenare forced into contact with one another and chemically react to formsilicon dioxide which is deposited upon the wafers, such as typicalwafer 92, as a thin film. Because of the wide dispersion of flow acrossthe width of the wafers caused by rods 78, uniformity in the rate ofdeposition across the surface of the wafers is achieved. As is betterillustrated in FIG. 3, the gases which have passed rods 78, are confinedto flow between adjacent wafers, or in the case of the end wafers in thearrangement, between the end wafers and end walls 77, 81, and 79, 83 ofcontainer 70. Horizontal flow within container 70 is prevented becauseof the end walls and the wafers. It should also be apparent that sincegas is entering conduits 46, 56 from opposite directions, the localizedvolumetric flow rate between adjacent wafers is maintained substantiallyequivalent. Valves 40, 54 are used to compensate for different pathlengths from the gas tanks to the opposite ends of conduits 46, 56 andmay be adjusted to "fine tune" the volume of gas entering from oppositeends of the conduits in order to thereby optimize the local flow ratesbetween wafers.

While the above-described method is the preferred one of maintainingsubstantially equivalent localized volumetric flow rate between adjacentwafers, it is within the scope of the invention to inject the gases fromonly one end of conduits 46, 56, the other ends being sealed. In thisalternative method, tapered slots may be provided in conduits 46, 56 sothat the widths of the resulting gas curtains vary with distance alongthe slots, thereby compensating for variation in the exit velocity ofthe gases with distance along the tapered slots. Still anotheralternative within the scope of the invention is to provide a pluralityof orifices along the length of conduits 46, 56 and spaced so as to bealigned with the spaces between adjacent wafers. In both alternativeembodiments, the dimensions of the tapered slots and the orifices,respectively, would determine the gas flow rates to be selected ontransducer/valves 38, 52, in order to achieve the desired filmdeposition rate.

It should also be noted that since gas is substantially prevented frompassing outside of confined region 89, and more specifically past walls72, 74 (FIG. 3), a substantially lesser amount of reactant gas isrequired than in the coonventional process since very little reactantgas is evacuated from tube 10 without having first contacted the siliconwafers.

As the gases chemically react to deposit the silicon dioxide film on thewafers, the unreacted gases and the exhaust gases of the chemicalreaction pass generally vertically upward between the wafers toward theupper portion of container 70 and into contact with rods 76. Rods 76create additional turbulence near the upper portion of the wafers andgenerally interrupt the gas flow, thereby causing some back flow whichprovides even greater dispersion of gas across the wafers. After thegases have passed the wafers and passed between the openings between thespaced-apart rods 76, the unreacted and exhaust gases pass outside ofcontainer 70 into the area between container 70 and the upper portion oftube 10. The unreacted and exhaust gases are evacuated from theenclosure by vacuum pump 12 in a generally horizontally flow directionabove container 70 towards the exit 14 of tube 10.

In order to better understand the above-described process for thedeposition of silicon dioxide as a dielectric isolation layer, a typicalrun will be explained with particular emphasis on the values of thevarious parameters involved. Typically, the pressure within tube 10 ismaintained at approximately 450-500 microns and the wafers are heated toapproximately 400°-500° Centigrade. Silane is introduced into the tubeat a flow rate of approximately 50 cubic centimeters per minute andoxygen at a flow rate of approximately 125 cubic centimeters per minute.Slots 60, 62 have a constant width of 0.010 inches in this example. Withthese values of pressure, temperature and gas flow rates, the aboveprocess provides a silicon dioxide film deposition rate of 400 Angstromsper minute with uniformity in film thickness within each wafer and fromwafer-to-wafer of plus or minus two percent.

In the event it is desired to introduce a dopant gas in theabovedescribed process, for example to provide the silicon dioxide filmwith resistance to cracking or to make it easier to flow, the dopantgas, such as phosphene (PH₃), is mixed with the second reactant gas,i.e. oxygen, prior to the introduction of the second reactant gas intotube 10. The programmable flow controller 61 controls transducer/valve64 so that the phosphene is mixed with the oxygen according to apredetermined ratio by weight, the respective optimum flow rates ofoxygen and phosphene having been previously determined empirically.

While the process has been explained in conjunction with the depositionof a thin film of silicon dioxide as a dielectric isolation layer on thesilicon wafers, it should be apparent that numerous other types of thinfilms can be deposited equally as well and with the same uniformity infilm thickness within each wafer and among the wafers in eacharrangement. For example, introducing dichlorosilane (SiH₂ Cl₂) andnitrous oxide (N₂ O), while maintaining the temperature of the wafers inthe range of 850 to 950 degrees Centrigrade results in the deposition ofsilicon dioxide as the initial insulating oxide layer on the wafers.Also, if silane alone is introduced while the wafers are maintained inthe range of approximately 800 degrees Centigrade, a thin film ofpolysilicon is deposited, the primary applications of which are as aninterstitial layer and as a dielectric isolation layer. Silicon nitrideand doped polysilicon are other examples of films which may bedeposited.

It should now be apparent that the above invention provides a new andsubstantially improved apparatus and process for the deposition of thinfilms on silicon wafers in the fabrication of integrated circuits. Sincethe reactant gas is introduced in close proximity to the silicon wafersin a direction parallel to the wafers before it is dispersed across theentire width of the wafers, increased deposition rate and betteruniformity of film thickness within individual wafers is achieved.Additionally, since the localized volumetric flow rate between adjacentwafers is generally the same, the uniformity in film deposition rate andin ultimate film thickness among the wafers in each wafer arrangement isalso greatly improved. Because the reactant gas is introduced into agenerally confined region on one side of the wafer arrangement and isthen forced to flow parallel and between adjacent wafers, less reactantgas is required, the use of a carrier gas is eliminated, and thetemperatures of the wafers can be maintained substantially equal,thereby minimizing the amount of energy used in the process.

While the preferred embodiments of the present invention have beenillustrated in detail, it should be apparent that modifications andadaptations of those embodiments will occur to those skilled in the art.However, it is to be expressly understood that such modifications andadaptations are within the sphere and scope of the present invention asset forth in the following claims.

What is claimed is:
 1. A process for the chemical vapor deposition offilms on silicon wafers comprising the steps of:providing asubstantially evacuated enclosure for the wafers and maintaining thepressure within the enclosure substantially below atmospheric; directingthermal radiation into the interior of the enclosure to heat the wafers;supporting the wafers within the enclosure in a spaced-apart mutuallyparallel arrangement with the central axes normal to the wafers beinggenerally collinear and with the planes defined by the wafers beingoriented vertically; introducing a reactant gas into the enclosure byfirst directing the gas horizontally from both ends of the length of thewafer arrangement simultaneously in a stream confined from the enclosureinterior and then generating from said stream a single substantiallyvertically oriented curtain of gas flowing into the enclosure interioralong the length of one side of the wafer arrangement; prior to thepassage of the flowing gas between the wafers, generating turbulence inthe flow so as to facilitate the later deposition of film on the wafers;after the gas has passed between the wafers and a portion of the gas haschemically reacted to deposit a film on the wafers, generatingturbulence in the flow near the side of the wafer arrangement oppositethe side where the gas was introduced to further facilitate thedeposition of film on the wafers; and removing the exhaust gas from theenclosure in a generally horizontal direction of flow.
 2. The processaccording to claim 1 including the step of preventing the gas fromflowing horizontally past the two end wafers of the wafer arrangement.3. The process according to claim 1 wherein the film to be deposited onthe wafers is polysilicon and wherein the step of introducing thereactant gas includes the step of introducing silane.
 4. The processaccording to claim 3 wherein the polysilicon film to be deposited on thewafers includes a dopant and including the step of mixing a dopant gaswith the silane in a predetermined ratio by weight prior to introducingthe silane.
 5. A process for the chemical vapor deposition of films onsilicon wafers comprising the steps of:providing a substantiallyevacuated enclosure for the wafers and maintaining the pressure withinthe enclosure substantially below atmospheric; directing thermalradiation into the interior of the enclosure to heat the wafers;supporting the wafers within the enclosure in a spaced-apart mutuallyparallel arrangement with the central axes normal to the wafers beinggenerally collinear and with the planes defined by the wafers beingoriented vertically; introducing a first reactant gas into the enclosureby first directing the first reactant gas horizontally from both ends ofthe length the wafer arrangement simultaneously, and then generating asingle substantially vertically oriented curtain of flowing firstreactant gas along the length of one side of the wafer arrangement;introducing a second reactant gas into the enclosure by first directingthe second reactant gas horizontally from both ends of the length of thewafer arrangement simultaneously, and then generating a singlesubstantially vertically oriented curtain of second reactant gas alongthe length of one side of the wafer arrangement and generally parallelto the curtain of flowing first reactant gas; just prior to the passageof the upwardly flowing gases between the wafers, generating turbulencein the flow of the gases so as to mix the first gas with the second gasand thereby facilitate the chemical reaction of the gases and thedeposition of a product of the chemical reaction as a film on thewafers; after the gases have passed between the wafers and a portion ofthe gases has chemically reacted to deposit a film on the wafers,generating turbulence in the flow near the side of the wafer arrangementopposite the side where the gases were introduced to further facilitatethe deposition of film on the wafers; and removing the exhaust andunreacted gases from the enclosure in a generally horizontal directionof flow.
 6. The process according to claim 5 wherein the film to bedeposited on the wafers is silicon dioxide, wherein the step ofintroducing the first reactant gas includes the step of introducingsilane, wherein the step of introducing the second reactant gas includesthe step of introducing oxygen, and wherein the step of directingthermal radiation includes the step of maintaining the temperature ofthe wafers within the range of 375-450 degrees Centigrade.
 7. Theprocess according to claim 5 wherein the film to be deposited on thewafers is silicon dioxide, wherein the step of introducing the firstreactant gas includes the step of introducing dichlorosilane, whereinthe step of introducing the second reactant gas includes the step ofintroducing nitrous oxide, and wherein the step of directing thermalradiation includes the step of maintaining the temperature of the waferswithin the range of 850-950 degrees Centigrade.
 8. The process accordingto claim 6 wherein the silicon dioxide film to be deposited includes adopant and including the step of mixing a dopant gas with the oxygen ina predetermined ratio by weight prior to introducing the second reactantgas.